Course code Course name - pce-fet.com · NODEB (softer handover) or in the RNC (SHO) improves the...

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Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.

3G Overview

Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved. Page2

WCDMA System Architecture

RNS

RNC

RNS

RNC

Core Network

Node B Node B Node B Node B

Iu-CS Iu-PS

Iur

Iub Iub Iub Iub

CN

RAN

UE Uu

CS PS


Multiple Access Technology and Duplex

Technology Multiple access technology

Time division multiple access (TDMA)

Frequency division multiple access (FDMA)

Code division multiple access (CDMA)

Duplex technology

Time division duplex (TDD)

Frequency division duplex (FDD)


FREQUENCY DIVISION MULTIPLE ACCESS (FDMA)

Frequency Division Multiple Access (FDMA) is common in the first generation of mobile

communication systems, so called analogue systems. The available spectrum in FDMA is

divided into physical channels of equal bandwidth.

One physical channel is allocated per subscriber. In pure FDMA systems, different

speech/data/signaling (per subscriber) transmissions may be transmitted at the same time on

different frequencies. The physical channel allocated to the subscriber is used during the entire

duration of the call and is unavailable for other subscribers during that time. The physical

channel is released at the end of the call and is then available for the next subscriber. In

summary, in FDMA, narrow bandwidth is used for continuous transmission and reception, there

is orthogonality in frequency within the cell, and no synchronization in time is needed.


TIME DIVISION MULTIPLE ACCESS (TDMA)

In TDMA, the available frequency is divided into units, which correspond to units of time,

known as time slots. Each subscriber requiring resources is allocated a unit of time (time slot)

during which they can transmit or receive data. The TDMA system is used in many Second

Generation (2G) systems such as GSM .

Power

Traffic channels: different time slots

are allocated to different users, for

example, DAMPS and GSM


CODE DIVISION MULTIPLE ACCESS (CDMA)

In CDMA, all subscribers share the same frequency at the same time within a

cell, so there is a need to distinguish between the different calls or sessions. The

information for each user is spread across the spectrum band using a unique

code. Spreading

means that the information is multiplied by codes.


WCDMA Frequency Band


Spreading Technology

Data bit

OVSF

code

Scrambling

code

Chips after

spreading


Channelization Code


Code correlation using Channelization

Codes (1/2)


Code correlation using Channelization

Codes (2/2)


Scrambling Code


Spreading Technology


Scrambling Code Planning

The number of codes used in the downlink is restricted to 8192 in total. 512 of these are primary codes (the rest are secondary codes, 15 codes per primary) divided into 64 code groups each group containing 8 different codes.


Channelization Code And Scrambling

Code Summary

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Classification of Handover

Hard handover

Soft handover

•Intra-frequency

hard handover

•Inter-frequency

hard handover

•Inter-system

handover Softer handover


WCDMA without Soft Handover


WCDMA with Soft Handover


Soft Handover

Features of soft handover

Seamless handover with no disconnection of the radio access bearer.

To enable a sufficient reception level for maintaining communications by

combining the received signal at symbol level from multiple cells in case

the UE moves to the cell boundary areas.

The macro diversity gain achieved by combining the received signal in the

NODEB (softer handover) or in the RNC (SHO) improves the uplink signal

quality and thus decrease the required transmission power of the UE.


Softer Handover

For soft handover, the combination of multiple RL uses

maximum ratio combination (RAKE combination) in downlink

and selection combination in uplink.

When the two cells in soft handover belong to the same NodeB,

maximum ratio combination could be used in uplink. In this

case the handover is softer handover.

Softer handover has higher priority in handover schemes

because maximum ratio combination has larger gain than

selection combination.


Soft Handover Measurement

Active set

Including all cells currently participating in a SHO

connection of a terminal.

Neighbor Set/Monitored Set

This set includes all cells being continuously

monitored/measured by the UE and which are not currently

included in the active set.


Node B

RNC

AirBridge

AirBridge

AirBridge

Soft Handover flow

Core

Network


Node B

RNC

AirBridge

AirBridge

AirBridge

Merged in NodeB

Soft Handover flow Core

Network


Merged in RNC

Node B

RNC

AirBridge

AirBridge

AirBridge

Soft Handover flow

Core

Network


Soft Handover flow (SRNC-DRNC)

Merged in SRNC

Node B

AirBridge

AirBridge

AirBridge

Serving RNC

Drift RNC

Core

Network


Soft Handover flow (SRN Relocation)

Node B

AirBridge

AirBridge

AirBridge

Serving RNC

RNC

Core

Network


Soft Handover Measurement


Hard Handover

Features of hard handover:

HHO causes a temporary disconnection for radio access bearer

and is lossless for NRT bearers.

The UE must either be equipped with a second receiver or support

compressed mode to execute inter-system/inter-system

measurement.

CM is to stop the normal transmission and reception for a certain

period of time, enable the UE to measure on the other frequency.

UE move

Target BS Source BS

time

Data UE received/

sent

“GAP” of communication


Introduction of Compressed Mode

Compressed Mode

Intra-frequency neighbors can be measured simultaneously

with normal transmission by UE using a RAKE receiver.

Inter-frequency or inter-system neighbors measurements

require the UE measuring on a different frequency, this has

either to be done with multiple receivers in the UE or in the

compressed mode.

CM is to stop the normal transmission and reception for a

certain period of time, enable the UE to measure on the

other frequency.


Compressed Mode

Objective of compressed mode: for UE to realize measurement and

synchronization to target cell when inter-frequency handover and

inter-system handover is required.


Capacity Limitation (1/2)


Capacity Limitation (2/2)


Admission Control

The purpose of Admission Control is to selectively deny access request in order to limit the load, and so avoids excessive triggering of congestion control.


Admission Control (AC)

AC is used to decide whether a new RAB is admitted

or a current RAB can be modified.

Admission control is done in uplink and downlink

separately.

The strategy is that a new bearer is admitted only if

the total load after admittance stays below the

threshold defined by RNP.


Load Balance

Load balance between cells

Load balance between intra-frequency cells

− Cell breathing

Load balance between inter-frequency cells

− Inter-frequency load balance


Cell Breathing

CRNC

The objective of load The objective of load

banlance is to share the banlance is to share the

load of some "hot" cells load of some "hot" cells

in surrounding cells with in surrounding cells with

low load, thus to low load, thus to

increase the usage of increase the usage of

system capacity.system capacity.

cell breathing


SRNC/DRNC

SRNC and DRNC are on a per connection basis between a UE and

the UTRAN

The SRNC handles the connection to one UE, and may borrow

radio resources of a certain cell from the DRNC

Drift RNSs support the Serving RNS by providing radio resources

A UE in connection state has at least one and only one SRNC, but

can has 0 or multiple DRNCs

CN

SRNC DRNC

Iu Iur


Random Access Procedure

Random access is a process where a UE requests access to the system, and the network answers the request and allocates a dedicated channel to the UE. It is important to minimize the transmitted power during the random access because excessive power will degrade the WCDMA system capacity.


Power Control

Power control is necessary in any spread spectrum system to ensure that each user transmits and receives just about the right amount of power to maintain the connection quality while at the same time causing as little interference as possible to other users.

The output power of the UE is then adjusted at a rate of 1500 times per second.

Thank you www.huawei.com

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